The present invention is in the field of battery technology and, more particularly, in the area of improved active materials for use in electrodes in electrochemical cells.
Research into active materials for cathodes for secondary batteries has yielded several classes of active materials. One class of these active materials, which are commonly used in portable electronics, is lithium cobalt oxide, producing a cathode half-reaction during discharge as follows:Li1-xCoO2+xLi++xe−↔LiCoO2  (i)
Lithium cobalt oxide cathode materials have high energy densities and relatively stable capacities. However, one of the major drawbacks to lithium cobalt oxide cathode materials is that only about 50% of the lithium ions present in the cathode can be used before the reduced cobalt cannot be re-oxidized and a permanent phase transition occurs. The electrochemical change to the cobalt and the permanent phase transition reduce the capability of the cathode to accept lithium ions during discharging. The result is a permanent reduction in cell performance. Notably, there is a permanent loss of reversible capacity.
There have been prior attempts to mitigate the reduction in cell performance and the permanent loss of capacity, but such efforts have met with limited success. For example, Zou et al. have experimented with doping LiCoO2 for high voltage cycling (that is, cycling up to about 4.5V) (see, Zuo et al., “Synthesis of High-Voltage (4.5V) Cycling Doped LiCoO2 for Use in Lithium Rechargeable Cells”, Chem. Mater., 2003, 15, 4699-4702.). Luo et al. have experimented with magnesium substituted LiCoO2 (see, Luo et al., “Synthesis and Characterization of Mg Substituted LiCoO2”, Journal of the Electrochemical Society, 2010, 157, A782-A790). Koyama et al. discuss the theoretical limits of doping LiCoO2 with various compounds (see, Koyama et al. “First Principles Study of Dopant Solubility and Defect Chemistry in LiCoO2” Koyama et al., J. Mater. Chem. A, 2014, 2, 11235). Kazada et al. have experimented with doping LiCoO2 with sodium and potassium (see, Kazada et al. “Comparison of Material Properties of LiCoO2 Doped with Sodium and Potassium”, Portugaliae Electrochimica Acta, 2013, 31, 331-336). Wang et al. have experimented with Mg doping on LiCoO2 in conjunction with a zirconium oxyfluoride coating (see, Wang et al. “Improving the cycling stability of LiCoO2 at 4.5V through co-modification by Mg doping and zirconium oxyfluoride coating”, Ceramics International, 2015, 41, 469-474). Chandrasekaran et al. synthesized a cathode containing LiCoO2 and various dopants (see, Chandrasekaran et al. “High-performing LiMgxCuyCo1-x-yO2 Cathode Material for Lithium Rechargeable Batteries”, ACS Appl. Mater. Interfaces 2012, 4, 4040-4046).
Despite ongoing research into electrode constructions that theoretically may allow for greater utilization of lithium ions without diminished future capacity, there remains a need for lithium cobalt oxide based cathode materials with improved capacity throughout the battery cycle life.